Synthesis and Structure of 3-formylquinoline-2(1H)-thione and -selone and the Corresponding Imines

3-Formylquinoline-2(1H)-thione and -selone have been prepared; based on ¹H, ¹³C and ¹⁵N NMR, UV and IR spectral studies the tautomeric form with a proton located at the heterocyclic nitrogen has been proved to be the most stable for the above aldehydes and their imines in both the solid state and in solution